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Aug." 28'; ' 1962 E. M. GYORGY ETAL 3,051,917 METHOD OF SUPPRESSING SATURATION EFFECTS IN GYROMAGNETIC DEVICES Filed June 22, 1960 2 Sheets-Sheet 1 FIG. / I A I ii : z /o SMALL S/GNAL RESPONSE | 9 : ‘<2D || Z + E 2 i / ,/. I | I / ~\ ' \ ~ i // LARGE SIGNAL RESPONSE | / i | HS Hm APPLIED MAGNETIC FIELD FIG. 2A FIG. 2B ' I i | | (AT0ENUcIO) A | 3, * B/ASED } 5/45/50 BELOW 2 I To MA/N ] | MAIN amoMAGNET/C 9 '; : | RESONANCE (Hm) : RESONANCE 2 l | w | I- | | F< I | | I | l PCRITICAL Pcz POWER INPUT POWER INPUT FIG. 3 as- 34 ‘\ ' -> M_ II ‘ N / W?" 35 W" 'H' / x" s 32/- // //’/ \I/// 1 JI ,/ 3/ GVROMAG/VE 77C MArER/AL < . E. M. GVORGV WE” TORS'H. E. 0. SCOVIL “WW/M A TTORNEV ' A'u"g.'28, 1962 3,051,917 E. M. GYORGY ETAL METHOD OF SUPPRESSING SATURATION EFFECTS IN GYROMAGNETIC DEVICES Filed June 22, 1960 2 Sheets-Sheet 2 . E. M GVORGV WVENTZRS'H. E. 0. sea V/L V W/j?D/K’NEV 07/ $51,917 United States Patented Aug. 28, 1962 2 1 1957. 3,051,917 At high power levels the coupling of energy from the uniform precession to the spin waves is en METHOD OF SUPPRESSING SATURATIGN hanced, substantially modifying the transmission prop EFFECTS IN GYROMAGNETIC DEVICES erties of the gyromagnetic material. ‘It is, accordingly, a more speci?c object of this inven Ernst M. Gyorgy, Morris Plains, and Henry E. D. Scovil, New Vernon, N.J., assignors to Bell Telephone Labora tories, Incorporated, New York, N.Y., a corporation of New York tion to inhibit the transfer of power between the uni form precession and the short wavelength spin waves. Investigation has shown that the spin waves propagate within the gyromagnetic material in a preferred direc tion with respect to the uniform precession, and have a ?nite build-up time. In accordance with the invention, This invention relates to electromagnetic wave devices means are provided whereby the direction of the uniform using gyromagnetic materials and, in particular, to means precession is changed at intervals comparable to or less for eliminating the anomalous attenuation etfects pro than the build-up time of the spin waves. By so modulat duced by such gyromagnetic materials at high power 15 ing the sense of the uniform precession there is insuf?cient levels. coupling between the uniform precession and the spin It has been observed that materials of the type having waves to enable their growth and propagation within the the properties described by the mathematical analysis Filed June 22, 196i}, Ser. No. 38,938 8 Claims. (Cl. 33>3—3l) of D. Polder, Philosophical Magazine, volume 40, pages 99 through 115 (1949'), have certain anomalous attenua tion characteristics which were not predicted by Polder’s theory. This class of materials, a chief one ‘among them being ferrite, is characterized by certain unpaired electron spins which respond to a transmitted microwave signal by precessing gyroscopically about the line of an applied magnetic ?eld. The interaction of these precession elec gyromagnetic material. The suppression of the above mentioned short wavelength spin waves effectively avoids the so-called anomalous large-signal behavior of gyro magnetic materials. The above-stated and other objects and advantages, the nature of the present invention, and its various fea tures, ‘will appear more fully upon consideration of the 25 various illustrative embodiments now to be described in trons with the applied microwave signal results in cer detail in connection with the accompanying drawings, in tain magnetic properties which have given these materials which: FIG. 1, given for the purpose of explanation, is a the name “gyromagnetic.” Polder’s so-called “small graphical and qualitative representation of the attenua signal” theory predicts an attenuation characteristic as shown by the solid curve ~10 in FIG. 1 of the drawings. 30 tion versus applied magnetic ?eld characteristic of gyro magnetic media showing the small signal and large Also shown in FIG. 1 is dashed curve 11 representing what signal responses; may be called the large signal response of gyromagnetic FIGS. 2a and 2b, given for the purpose of explanation, materials. It will be observed that the large signal re are graphical and qualitative representations of the at sponse exhibits certain anomalous characteristics in the regions .of two particular applied ?eld values which are 35 tenuation versus applied power characteristics of gyro magnetic media at the ?eld values HS and Hm, respec not predicted by Polder’s theory and are not present at tively, shown in FIG. 1; smaller signal levels. Thus, at the ?eld value HS, the at FIG. 3 is a perspective view of an illustrative embodi tenuation for large signals is much greater than for ment of the invention in which the modulating ?eld is small signal-s, while at another ?eld value Hm, the attenua applied in the direction opposite to the magnetizing ?eld; tion for large signals is much less than that for small FIG. 4, given by way of explanation, is a graph show signals. This large signal behavior of gyromagnetic ma ing the hysteresis loop of a typical sample of gyromag terials has been observed by R. W. Damon, Review of netic material; Modern Physics, volume 25, pages 239 through 245, Jan ‘FIG. 5 is a perspective view of a second embodiment uary 1953, and by N. Bloembergen and S. Wang, Physi 45 of the invention in which the modulating ?eld is applied cal5 Review, volume 93, pages 72 through 83, January oblique to the biasing ?eld; 19 4. FIG. 6 shows a third embodiment of the invention il The effect of this large signal behavior has been to lustrative of a method of reducing instantaneous varia severely limit the operating range of electromagnetic tions in the transmission properties of microwave devices wave devices employing gyromagnetic materials. produced by the modulating ?eld; and Gyromagnetic devices can be broadly divided into two ‘FIG. 7, given by way of explanation, shows the man classes: those biased below gyromagnetic resonance and ner in which the instantaneous phase shift of the device which depend for their operation upon the effective shown in FIG. 6 varies under the in?uence of the modu permeability of the gyromagnetic element and its low attenuation, and those biased at resonance and which de 55 lating ?eld. Referring more particularly to FIG. 1, there is shown, pend upon the effective high attenuation of the gyromag for the purpose of explanation, a graphical and qualita netic element. tive representation of the attenuation (a) as a function of Because the so-called “large signal” effects can, in fact, the applied magnetic biasing ?eld characteristic of gyro occur at relatively low power levels, the performance of both classes of devices over a substantial range of op 60 magnetic materials. The term “gyromagnetic material” is employed here in its accepted sense as designating the erating signal levels is adversely effected by the anomalous class of magnetic polarizable materials having unpaired characteristics of gyrornagnetic materials. spin systems involving portions of the atoms thereof that It is, therefore, an object of this invention to avoid the are capable of being aligned by an external magnetic so-called “large signal” behavior of gyromagnetic ma polarizing ?eld and which exhibit a signi?cant preces terials. 65 sional motion at a frequency within the range contem~ The anomalous behavior of gyromagnetic materials at plated by the invention under the combined in?uence of high power levels has been explained as due to the excita said polarizing ?eld and a varying magnetic ?eld com ponent. This precessional motion is characterized as entitled “The Theory of Ferromagnetic Resonance at 70 having an angular momentum and a magnetic moment. Typical of such materials are the ferromagnetic materials High Signal Powers,” The Journal of the Physics and including the spinels such as magnesium aluminum fer Chemistry of Solids, volume 1, pages 209-227, April tion within the material of a class of short wavelength spin waves. (This is discussed by H. Suhl in an article 3,051,917 3 4 rite, aluminum zinc ferrite and the garnet-like materials the microwave signal has not increased appreciably. So such as yttrium-iron garnet. far the conditions have remained within the scope of the _ Solid curve 10 shows this characteristic for small signal levels below a critical value, to be discussed more fully below, and dashed curve 11 shows this characteristic for large signal levels above the critical value: The behavior of a gyromagnetic medium for small signals has been explained on the-theory that in the presence of an ap plied magnetic ?eld having an amplitude great enough-to small signal theory. As the power level of the applied signal continues to increase, however, a critical point is reached where the preferred band of spin waves can no longer transfer en ergy to the remainder of the spin Wave system as fast as it is being received from the uniform precession. At this point, called the critical power level, the preferred band saturate the magnetic material, the unpaired electron spms 10 goes to a higher state of excitation to accommodate the in the medium line up parallel to one another and tend to behave gyroscopically as a single unit. Therefore, when increase in energy level. The excitation of the preferred band tends to build up rapidly since the coupling thereto the frequency of the applied signal is equal to the natural is nonlinear, increasing with increasing signal level. This precession frequency of the electron spins, a resonant band, being resonant with the uniform precession, is now condition exists under which the electron spins are able 15 more strongly coupled to the uniform precession and to absorb large amounts of energy from the signal. This therefore receives even more energy from the uniform condition, which has been called the main gyromagnetic precession. This further increases the excitation level resonance, is shown at the applied ?eld value Hm in FIG. of the preferred band, allowing even further amounts of 1. At all other ?eld values the attenuation is very low energy to be coupled thereto. This build-up cycle con and may be neglected. 20 tinues until the power absorbed by the preferred band is The simple uniform precession theory used above, how just su?icient to balance the losses of the resonant system. ever, does not explain the shape of the attenuation charac teristic at large signal levels, represented by dashed curve 11 in FIG. 1. At these large signal levels, the attenuation at main resonance becomes substantially lower and the resonance curve becomes substantially broader than at small signal levels. Furthermore, a second resonance, which may be termed the subsidiary resonance, appears at It can be seen that an unstable condition exists at the critical power level which results in large amounts of energy being absorbed from the applied signal. This re sults in a large increase in the attenuation offered to the applied signal. Any further increase in the power level of the applied signal is substantially all diverted into the an applied ?eld value of HS, substantially less than Hm. An attempt will be made below to explain this anomalous preferred spin wave band. This condition is shown as the subsidiary resonance hump in dashed curve 11 of FIG. 1 at applied ?eld value H5. The change in attenuation behavior of polarized gyromagnetic media at high sig can more readily be seen in FIG. 2a. nal levels. The small signal theory states that a microwave signal passing through a polarized gyromagnetic medium is cou pled to the electron spins within the medium by means of In FIG. 2a there is shown, for the purpose of explana tion, a graphical and qualitative representation of the at the high frequency magnetic ?eld components of the applied signal. The electron spins are thus driven en masse to precess gyroscopically at some angle about the line of the applied magnetic ?eld. Not taken into ac count by this small signal theory is the coupling between this uniform precession of the electron spins and certain small perturbances in the electron spin system which may tenuation versus power input characteristic of a gyro magnetic medium biased to a ?eld value Hs as shown in FIG. 1. It can be seen that the attenuation is very low for power inputs below the critical power PM. At this point, however, the attenuation suddenly jumps to a very high value due to the resonance between the uniform precession and the preferred spin wave band. Beyond this point the attenuation decreases slightly but retains substantially its high value. The power level at which be called spin waves. the run-away condition occurs is a function of the mag A gyromagnetic medium is continually in a state of netic state of the gyromagnetic medium and the relaxa thermal agitation, resulting in a minute and somewhat 45 tion time of the preferred spin Waves. random misalignment of the electron spins. These per In the case of the main resonance at an applied mag turbances can, by means of a Fourier analysis, be resolved netic ?eld of Hm, the uniform precession is again cou— into a series of waves, called “spin Waves,” which are all pled to a preferred band of spin Waves having a fre coupled to each other and to the uniform precession by quency and direction of resonance closely resembling that means of interspin magnetic forces and electrostatic of the uniform precession. Under this condition, how forces called exchange ?elds. A relatively narrow band ever, the uniform precession is already absorbing large of these spin waves, which may be called the preferred amounts of energy from the applied signal and is there band, is much more strongly coupled to the uniform pre fore near its maximum state of excitation. When the cession than the remainder of the spin waves due to a critical power level is reached and the preferred spin correspondence between their resonances in frequency and 55 wave band can no longer get rid of energy as fast as it direction. The spin wave system, and especially the pre receives it, the preferred spin waves go to a higher state ferred band, can, by means of this coupling, absorb energy of excitation at the expense of the uniform precession. from the uniform precession. However, under conditions The removal of energy from the uniform precession de within the scope of the small signal theory, the energy loss creases the coupling of this precession to the applied sig to the spin wave system is su?iciently small to be negli 60 nal and hence the attenuation olfered to the signal also gible. decreases. Further increases in the power level of the The condition of subsidiary resonance, represented by HS in FIG. ll, will now be investigated. When biased be applied signal result in further excitation of the preferred spin waves and a larger decoupling of the uniform preces sion from the applied signal. The attenuation therefore coupled to the uniform precession due to the lack of 65 decreases and eventually goes to zero when the uniform low resonance, only very small amounts of energy can be correspondence between the applied frequency and the precession is completely decoupled from the applied sig natural resonant frequency of the uniform precession. nal. This condition is shown as the decline and broaden However, a small increase in the applied signal will ing of the main resonance peak in dashed curve 11 of nevertheless raise the excitation of the uniform precession FIG. 1 at applied ?eld value Hm. The change in attenua slightly, allowing small amounts of energy to be trans 70 tion can more readily be seen by considering FIG. 2b. ferred to the preferred spin wave band and thence to the In FIG. 2b there is shown, for the purpose of explana remainder of the spin wave system. Eventually this en tion, a graphical and qualitative representation of the at ergy is transmitted to the crystal lattice to be dissipated as tenuation versus power input characteristic of a gyro heat. Since the excitation level of the spin wave system magnetic medium biased by a ?eld Hm as shown in FIG. 1. has not changed appreciably, the attenuation offered to 75 It can be seen that the attenuation is very high for 3,051,917 power inputs below the critical power P02. At this point, however, the attenuation suddenly drops to a low value. 6 past vane 31 with substantially little or no ‘attenuation. Under this condition source 36 is gated off. As the power level of the propagating wave increases and approaches Thereafter, the attenuation continues to decrease, ap the critical power level, source 36 is gated on. The out proaching zero. The critical power level at which the de put of source 36 is a wave having an amplitude and fre cline in attenuation begins has been found to be governed quency to reverse the direction of magnetization at a by the same factors as govern the critical power level at rate related to the spin wave build-up time in vane 31. subsidiary resonance. To determine the amplitude of the modulating ?eld In FIG. 3 a reciprocal phase shifter is shown, modi?ed necessary to reverse the magnetization when the magnetic in accordance with the invention to eliminate subsidiary resonance effects and to thereby produce low-loss phase 10 material is biased at or above saturation, reference is made to ‘FIG. 4 which shows a typical hysteresis loop shift at radio frequency power levels substantially greater for the gyromagnetic material. Speci?cally, FIG. 4 than the critical power level for the gyromagnetic ma shows the relationship between the magnetomotive force or magnetizing ?eld H and the magnetic ?ux density B. wave energy, which may be a rectangular waveguide of 15 Assuming the biasing magnetization to be -—Hd.c, the magnetic state of the material is that given by point the metallic shield type having a .wide internal cross-sec (1) on FIG. 4. To reduce the magnetic ?ux, B, to zero tional dimension of at least one-half wavelength of the from point (1) would require a reverse magnetomotive wave energy to be conducted thereby and ‘a narrow di force of Hc-l-Hdc, where Hc is the coercive force for mension substantially one-half of the wide dimension. Included within guide 30‘ are means for imparting a 20 the material. This is indicated at point (2). To now reverse the magnetic ?ux in the magnetic material phase delay to the wave energy propagating therethrough. terial. Speci?cally, the phase shifter comprises a guide 30 of ‘bounded electrical transmission line for guiding In particular, disposed within guide 30 is a thin vane 31 of gyromagnetic material. Vane 31 is symmetrically dis to some point (3), the application of an additional mag netomotive force AH is necessary. It should be noted, however, that to go from state equally spaced from both narrow walls, with the long di 25 (1) to state (3) requires a ?nite time. The mere ap plication of a reverse magnetomotive force will not, mension of vane 31 extending longitudinally along the instantaneously, reverse the ?ux within the gyromagnetic guide, parallel to the guide walls. material. Since it is necessary for the purposes of the Vane 31 is biased by a steady magnetic ?eld at right invention to change the magnetization in a time that is angles to the direction of propagation of the wave energy short compared to the spin wave build-up time, the am 30 in guide 30. As illustrated in FIG. 3, this ?eld may be plitude of the reversing force must be adjusted accord supplied by an electrical solenoid having a magnetic core ingly. Speci?cally, if the spin wave build-up time is 32 and pole pieces N and S bearing upon. the wide walls Tw, the switching time 'rs should be greater than Tw. The of guide 30- in a region substantially coextensive with the magnetomotive force Hm required to switch at this rate gyromagnetic vane 31. Turns of wire 33 are wound about core 32 and connected through a potentiometer 34 35 is then posed within guide 30 along the longitudinal guide axis to a source of magnetizing current 35. The operation of the phase shifter shown in FIG. 3 is based upon the effective permeability presented to the propagating wave. Since resonant absorption represents where SW, the switching coe?icient, and H0, the threshold a loss for these applications, these devices operate in a 40 ?eld, are constant of the material and are determined experimentally. A typical value of SW is 0.2 oe.;isec., range of applied magnetic ?elds between zero and that re while H0 is approximately equal to 2H6. The spin wave quired to initiate the resonant phenomenon. In particu build-up time, Tw, being a function of the material, its lar, the region of magnetic saturation is of primary im geometry and the radio frequency power level, is also portance since the effective permeability is greatest in this region. At power levels below the critical power level, 45 determined experimentally. This can be done by sud denly applying a radio frequency wave greater than the low-loss phase shift is readily obtained. However, above critical power level to the gyromagnetic element biased the critical power level coupling between the imiform below resonance. Momentarily the output will rise to magnetic precession and the spin waves gives rise to the full transmission. As power is coupled to the spin above-described subsidiary resonance effect which, for all practical purposes, substantially destroys the usefulness 50 waves and the spin waves build up, the output will ex ponentially fall off until a lower steady state output is of the phase shifter. reached. The time for the output to decline to approxi In accordance with the invention the tendency to cou mately 37 percent of the peak output is one time con ple energy to the spin waves is inhibited by changing the stant, or 'rw. In a preferred embodiment ¢S is made direction of magnetization within the gyromagnetic vane 31. In the embodiment of the invention shown in FIG. 55 equal to Tw/ 10. In the embodiment of the invention shown in FIG. 3, 3 this is done by modulating the steady biasing ?eld by given for the purpose of illustration, it is assumed that means of a high frequency signal having an amplitude the gyromagnetic material is transversely biased to satu and frequency which will be explained in greater detail ration and that the function of the microwave device is hereinafter. The modulating ?eld is impressed upon the magnetic ‘core 32 by turns of wire 37 which connect to a 60 to introduce phase shift. It is to be understood, however, that for the purposes of this invention the function of high frequency energy source 36. the device could just as well be to introduce attenuation For simplicity, source 36 is shown in FIG. 3 as a sepa into the microwave system and for that purpose the gyro rate generator. It is understood, however, that source 36 magnetic material is biased to gyromagnetic resonance. would generally be associated with 1a power level detec tor that would monitor the power level in guide 311 and 65 As was explained hereinbefore, when a resonantly biased attenuation is operated above the critical power level, only gate source 36 on when the power level in guide 30 the overall attenuation tends to decrease. By modulat exceeded the critical power level of the gyromagnetic ing the steady biasing ?eld, as explained hereinbefore, medium. coupling between the uniform precession and the spin In operation, potentiometer 34 is adjusted to produce a steady biasing ?eld having an amplitude su?iciently large 70 Waves is impeded and the tendency for the attenuation to decrease is avoided. to produce saturation in vane 31. So biased, the mag It will also be noted that in the illustrative embodi netization throughout the material is aligned parallel to ment of ‘FIG. 3 the modulating ?eld completely re the direction of the biasing ?eld. Wave energy, having verses the direction of the biasing ?eld. However, as an amplitude less than the critic-a1 amplitude for the gyro magnetic material, will propagate along guide 3%? and 75 was pointed out, it is only necessary to change the direc 3,051,917 7 e tion of the magnetization within the gyromagnetic ma terial. This would also include a change in direction less than 180 degrees. A modi?cation of the embodiJ ment of FIG. 3 wherein changes in the direction of magnetization less than 180 degrees are utilized as shown in FIG. 5. a pencil of gyromagnetic material disposed along the lon gitudinal axis of a rectangular section of waveguide. In this type of phase shifter the gyrornagnetic element is longitudinally biased below saturation. While modula— tion of the longitudinal magnetic ?eld in accordance with the principles of the invention will extend the power han The device shown in FIG. 5 comprises a section of waveguide 50, and a vane of gyromagnetic material 51 taneous phase shift produced by the device will also vary, disposed therein. thus introducing'what could ‘be an objectionable phase Vane 51 is biased by a steady mag dling capabilities of this type of phase shifter, the instan netic ?eld Hdc at right angles to the direction of propa~ 10 shift ripple in the output wave. gation of the wave energy in guide 50. This ?eld may This di?iculty, however, may be readily obviated by be supplied by an electric solenoid, by a permanent mag modifying the phase shifter as shown in FIG. 6. Speci? netic structure, or vane ‘51 may be permanently mag cally, the overall phase shift is obtained in two parts by netized if desired. dividing the gyromagnetic element into two portions and In the embodiment of FIG. 5 the steady biasing ?eld 15 separately controlling the magnetic ?elds applied to each Hdc is modulated by means of locally generated mag of the two portions. The phase shifter shown in FIG. 6 netic ?elds which tend to alter the direction of the bias comprises ‘a section of rectangular waveguide 60 within ing ?eld. These local ?elds are produced by means of which there are suitably supported two ‘cylindrical rods a conductive member 52 which is threaded through the 61 and 62 of gyromagnetic material. Rods 61 and 62 are gyromagnetic vane 51. As shown in FIG. 5, conductor 20 longitudinally disposed within guide 60 along the guide 52 lies in a plane perpendicular to the electric ?eld in axis and are longitudinally biased by means of solenoids guide 50 and passes through the broad surface of vane 63 and 64, respectively, mounted outside of waveguide 60. 51 over a region coextensive with the longitudinal di Solenoid 63 is connected through potentiometer 65 to a mension of the vane. Conductor 52 is energized by source of magnetizing current 66. Similarly, solenoid 64 means of the high frequency energy source 53. 25 is connected through potentiometer 67 to said source of As before, when the amplitude of the wave energy magnetizing current 66. is less than the critical level, source 53 is off. As the Since the rods are biased below saturation, the direction power level of the propagating wave increases and ap of magnetization is not parallel to the biasing ?eld but proaches the critical level, source 53 is gated on, ener instead varies throughout the volume of the rods. Thus, gizing conductor 52 and producing local magnetic ?elds 30 the instantaneous direction of magnetization can be varied about conductor 52 in the region of the gyromagnetic by merely varying the intensity of the biasing ?eld. Ac element. Speci?cally, the magnetic ?eld produced by cordingly, the modulating ?eld is applied parallel to the the modulating source 5-3 comprises closed loops 54 biasing ?eld by means of the two additional solenoids 68 surrounding conductor 52. The effect of these ?eld com and 69, each of which extends over a region of guide 60 ponents is to alter the direction of the net magnetic 35 substantially coextensive with one of the rods. Solenoids ?eld over most of the volume of the gyromagnetic vane, 68 and 69 are energized from the same high frequency thereby minimizing the tendency for energy to couple energy source 70. However, inserted in the circuit asso between the uniform precession and the spin waves. The amplitude of the modulating ?eld will depend upon the application; that is, if the device shown in FIG. 5 is a ciated with solenoid 69 is the phase shifter 71 for intro: ducing a 180 degree phase difference between the modu lating current in solenoid 69 and the modulating current in solenoid 68, as will be explained in greater detail here inafter. ‘Curve 80 of FIG. 7 shows the phase shift produced by each of the gyromagnetic rods, in the embodiment shown phase shifter, the amplitude of the modulating ?eld is adjusted so as to maintain the attenuation through the device below a speci?ed maximum for the given oper ating level. If, on the other hand, the device in FIG. 5 is intended to be a resonant attenuator, then the ampli tude of the biasing ?eld is adjusted so as to maintain the attenuation above a speci?ed minimum at the de in FIG. 6, as a function of the instantaneous magnetizing ?eld H. Assuming a total desired phase shift of 183 de grees, the magnetizing ?eld produced by solenoid 63 is adjusted to H1, producing a phase shift ,81 along rod 61, ing rate is related to the spin wave build-up time for the and the magnetizing ?eld produced by solenoid 64 is ad given gyromagnetic element. 50 justed to H2, producing a phase shift ,82 along rod 62, It is apparent from the above discussion that the net Where Bl+B2:B3 e?ective magnetization within the gyromagnetic element > As the amplitude of the wave energy propagating along sired operating level. As before, however, the modulat is varied as a function of time. While the desired effect guide 60 approaches the critical level, source 70 is ener of this variation is to disrupt the coupling between the gized subjecting rods 61 and 62 to a varying magnetic magnetization and the spin waves, it also tends to modu 55 ?eld component which modulates the phase shift pro late the instantaneous phase shift or attenuation produced duced by each of said rods. Let us consider rod 61 ?rst.‘ by the microwave device. If the resulting overall phase Under the in?uence of solenoid 68, the total magnetiz shifter the resulting overall attenuation is still su?icient ing ?eld within rod 61 will start to increase, causing the for the purpose intended, this modulation, or ripple, pro total phase shift produced by rod 61 to increase in ac duced by the modulating wave may be tolerable. If, how 60 cordance with the variation de?ned by curve 80. Let ever, the variations produced 'by the modulating wave are us assume that the total magnetizing ?eld for rod 61 in not permissible, corrective measures can be taken. Per creases to a point H1’. The total phase shift produced by haps the simplest corrective measure consists in cascading rod 61 is then increased to [31’. ‘Because of the 180 de a number of gyromagnetic elements and suitably phasing gree phase shift produced ‘by phase shifter 71, the effect the modulating ?eld impressed upon them so as to re 65 of the modulating ?eld produced by solenoid 69 is to re duce the net modulating ripple to a speci?ed minimum duce the total magnetizing ?eld in rod 62 from Hz to H2’, level. A simple embodiment of such an arrangement is causing the total phase shift in this section of the device shown in the structure of FIG. 6, which is basically a to decrease ‘from ,82 to ,6'2'. Because curve 80 is substan phase shifter of the type described by F. Reggia and E6. tially linear in the region under consideration, B1’+;82' is Spencer in ‘an article entitled “A New Technique in ‘Fer 70. substantially equal to til-H32. Thus, the total phase shift rite Phase Shifting for Beam Scanning of Microwave An- . through the two sections of the phase shifter remains sub tennas,” November 1957, Proceedings of the I.R.E., pages stantially constant even though the individual phase shift 1514-4517, modi?ed in accordance with the principles of in each section may vary instantaneously due to the effect the invention. ' of the modulating ?eld. It is obvious that by suitably The tic-called Reggia-Spencer phase shifter comprises 75 arranging the phasing of the modulating ?elds, the num 3,051,917 her of gyromagnetic rods may be increased and the total 1% for reversing the direction of said biasing ?eld at a phase shift divided among these additional rods, further reducing any ripple in the overall phase shift. rate l/TS greater than the reciprocal of the spin wave build-up time for said material, said reversing ?eld having In all cases it is understood that the above-described arrangements are illustrative of a small number of the an amplitude many possible speci?c embodiments which can represent applications of the principles of the invention. Numerous where H0 is the threshold ?eld for said material, and ‘SW is the switching coefficient. accordance with these principles by those skilled in the 6. The combination according to claim 5 wherein the ‘art without departing from the spirit and scope of the 10 switching rate l/¢s is approximately equal to 10‘/Tw invention. 7. A phase shifter for electromagnetic wave energ What is claimed is: comprising a section of conductively bounded waveguide 1. An electromagnetic wave transmission device com supportive of said wave energy, ?rst and second elongated prising a section of guided wave path having an element elements of ferromagnetic material disposed in longi 15 of ferromagnetic material disposed therein, said material tudinal succession within said waveguide, each of said characterized as having a ?rst transmission constant for and varied other arrangements can readily be devised in applied signals below a critical power level and a second transmission constant different than said ?rst constant for applied signals above said critical power level, said elements presenting a ?rst propagation constant to wave energy below a given power level and a second propaga tion constant to wave energy above said given power level, each ‘of said elements also having a given spin wave build material further characterized as having a given spin wave up time, means for longitudinally magnetizing said ?rst build-up time, means for establishing a given state of element at a ?rst ?eld intensity, means for longitudinally magnetization within said material, means for applying magnetizing said second element at a second ?eld intensity electromagnetic wave energy to said section of wave path greater than said ?rst intensity, where said ?rst and sec having a power level greater than said critical power ond intensities are less than that necessary to produce level, and means for preventing said material from assum saturation in said elements, means for applying electro ing said second transmission constant including means for magnetic wave energy to said waveguide having a power modulating said given state of magnetization at a rate not level greater than said given power level, and means less than the reciprocal of the spin wave build-up time of for increasing said ?rst ?eld intensity an incremental said material. 2. The combination according to claim 1 wherein the 30 amount AH, and means for decreasing said second ?eld intensity an incremental amount substantially equal to direction of magnetization within said material is reversed AH at a rate greater than the reciprocal of said given spin by said modulating means. wave build-up time for said elements with the variation ‘3. The combination according to claim 1 wherein the in said ?rst element being 180 degrees out of time phase direction of magnetization within said material is caused with respect to the variation in said second element. to change ‘by said modulating means by an amount less 8. A device for electromagnetic wave energy compris than 180 degrees. ing a section of conductively bounded waveguide sup 4. A high power, low-loss, microwave device includ portive of said wave energy, a plurality of n elements of ing an electromagnetic wave transmission path having a power saturable ferromagnetic medium disposed therein, ferromagnetic material disposed in longitudinal succes said medium characterized as having a low positive atten 40 sion within said Waveguide, each of said elements present ing a ?rst propagation constant to wave energy below a uation constant for applied signals below a critical power given power level and a second propagation constant to level, but capable of exhibiting a high positive attenuation wave energy above said given power level, each of said constant to signals above said critical power level, said elements also having a given spin wave build-up time, medium further characterized as having a given spin Wave build~up time, means for applying a steady magnetic . means for magnetically biasing each of said elements at a di?erent ?eld intensity, means for applying electro biasing ?eld to said medium, means for applying electro magnetic wave energy to said waveguide having a power magnetic wave energy to said path having a power level level greater than said given power level, and means for greater than said critical power level, and means for pre varying said different ?eld intensities at a rate greater venting said medium from exhibiting said high attenuation constant including means for modulating said magnetic 50 than the reciprocal of said given spin wave buid-up time for said elements with the variation in each of said ele ?eld at a rate not less than the reciprocal of the spin wave ments differing in phase by an amount equal to 360/ n build-up time of said medium. degree or whole multiples thereof. 5. A microwave phase shifter comprising a guided elec tromagnetic wave transmission path having an element References Cited in the ?le of this patent of ferromagnetic material disposed therein, said medium 55 UNITED STATES PATENTS characterized as having a low positive attenuation for applied signals below a critical power level but capable 2,798,205 Hogan ________________ __ July 2, 1957 of exhibiting a high positive attenuation to signals above 2,820,200 Du Pre ______________ __ Jan. 14, 1958 said critical power level, said medium further character 2,847,647 Zaleski ______________ __ Aug. 12, 1958 ized as having a given spin wave build-up time 'rw, means 60 for applying a steady magnetic biasing ?eld Hdc to said medium in a given direction, means for applying electro magnetic wave energy to said wave path having a power level greater than said critical power level, and means OTHER REFERENCES Wheeler: “IRE Transactions on Microwave Theory and Techniques,” January 1958, pages 38-39.